Molecularly imprinted polymers (MIPs) are polymers that can selectively recognize target molecules. This is achieved by allowing the target molecule, referred to as the template, to pre-assemble with certain monomers that have functional groups that can form non-covalent interactions with functional groups in the structure of the template. For example, functional monomers with positively charged functional groups can form electrostatic interactions with negatively charged side chains of amino acid residues on the surface of a protein. After pre-assembly, free radical polymerization is initiated and a polymer network with cavities that are complementary to the template in both shape and functionality is formed (FIG. 1). After thorough washing to remove the template from the polymer, the polymer can then selectively rebind to the template, similar to how an antibody would recognize its antigen. These polymers are used in a number of medical applications, including diagnostics, microsensors, biosensors, drug discovery, controlled release of drugs in response to interaction with the target molecule, and accelerated clearance of undesirable molecules from the body.
In recent years, many investigators have had a significant interest in discovering biomarkers that can be used for diagnostic tests. Biomarkers are indicators of the physiological state and change during a disease's progression. They reflect changes in the active genes of a cell and the products of these genes, such as proteins. Being able to sensitively detect these molecules at an early stage of a disease or before a recurrent flare could lead to more favorable treatment options and better prognoses. However, it has been a challenge to achieve this early detection and thus widespread use of diagnostic screening tests in the clinic has not yet been seen for a number of reasons. The current tests lack specificity and sensitivity, which are measures of how well the test can discern healthy people from people with the disease. Furthermore, these tests use proteins, specifically antibodies and enzymes, which are expensive and have poor shelf life. It will be necessary to develop a highly cost-effective diagnostic test, especially for regular, systematic mass screening that would be needed for them to be effective. Another disadvantage of current diagnostic techniques, such as biopsies, is that they can be invasive and uncomfortable for the patient. An alternative to this invasive technique is to use in vivo optical imaging techniques to identify biomarker levels and localization. These techniques involve the use of a recognitive material, typically an antibody, and a contrast reagent such a near infrared dye or gadolinium. These approaches, however, are limited due to, among other things, toxicity from injecting foreign antibodies and contrast agents into the body.